naked eye. He saw, a little to the left of a diameter passing through the highest point of the Moon's limb, a luminous spot composed of jets entwined in each other, and in appearance resembling a hank of thread in disorder.'

The accompanying picture (fig. 80) represents the

general phenomena seen during the eclipse of 1842; but it must be remembered, that such illustrations cannot be regarded as accurately representing details, because they are usually drawn after the eclipse is over, and represent merely what the observer remembers. Until the whole duration of a total eclipse is devoted by a skilful observer and draughtsman to the delineation of the corona, we cannot expect to have really trustworthy views.

During the eclipse of 1851 no observations were made which tended to throw new light on the nature of the corona. It is worthy of notice, however, that the Astronomer Royal found the aspect of the corona different from what he had noticed in 1842. The corona,' he says, 'was far broader than that which I saw in 1842. Roughly speaking, the breadth was little less than the Moon's diameter, but its outline was very irregular. I did not notice any beams projecting from it which deserved notice as much more conspicuous than the others; but the whole was beamy, radiated in structure, and terminated-though very indefinitely-in a way which reminded me of the ornament frequently placed round a mariner's compass. Its colour was white, or resembling that of Venus. I saw no flickering or unsteadiness of light. It was not separated from the Moon by any interval, nor had it any annular structure. It looked like a radiated luminous cloud behind the Moon.'

These observations, combined with what had been before noticed, seem to demonstrate that the aspect of the corona is variable according to the circumstances under which it is viewed. It does not seem to be established that the rotatory and flickering motions suspected by other observers were only optical illusions, though the observation of the steadiness of the corona by such an observer as the Astronomer Royal goes far to negative observations of motion by less experienced astronomers. In the case of a phenomenon like the

corona, it is easier to imagine movement in the ring of light than to become convinced of its fixedness.

The eclipse of 1858, visible in Brazil, is chiefly remarkable on account of the strange drawing made by the French astronomer Liais (fig. 81). Unfortunately we have no observations confirming the accuracy of this singular picture.

The eclipse of 1860 is remarkable as the first in

which the powers of photography were employed to aid in the resolution of the problems presented by the corona. It will be seen, on a reference to figs. 66 and 67, that Mr. De La Rue succeeded in obtaining traces of the corona. Those seen in Father Secchi's photographs are somewhat more distinct, the method he employed giving a smaller and more fully illuminated

image. In a third of Fr. Secchi's photographs (fig. 82) the corona is yet more distinctly shown.

The extension of the corona in fig. 82 is regarded by Fr. Secchi as corresponding to the solar equator, whose position is very nearly indicated by the cross-wire

The Eclipse of 1860. From a Photograph by Secchi.

shown in the figure. La couronne,' he says, 'est très-irrégulière, mais on peut remarquer qu'elle présente une étendue plus considérable à droite et à gauche que dans les autres directions, c'est-à-dire qu'elle est plus développée dans le plan de l'équateur (solaire) que suivant la ligne des pôles.' But, as Fr. Secchi himself points out further on, the figure indicates

rather an extension opposite four points lying between the equator and poles, than an extension at the equator. In fact, fig. 82 presents a very striking resemblance to Mr. Whipple's picture further on (fig. 85). It is worthy of notice, too, that not only does the outline of the corona present this quadrilateral aspect, but in the bright parts close to the Moon's limb there are four corresponding regions of greatest brilliancy. In the second of Mr. De La Rue's photographs the brightest portions seem similarly disposed.*

Some of the direct observations made in 1860 serve also to throw important light on the nature of the corona. To the Astronomer Royal the corona presented much the same aspect as in 1851. Bruhns of Leipsic states that when the last rays of the Sun disappeared, the corona shone out with a white light, of such brilliancy that the protuberances were almost

* One cannot wholly agree with Father Secchi's remark, that Mr. De La Rue's photographs afford no evidence of the peculiar quadrilateral expansion of the corona corresponding to the position of the zone of spots. It is true, however, that when Fr. Secchi published his results, astronomers did not conceal their doubts.' If the expansion of the corona in four directions be regarded as an ordinary phenomenon (and we have seen how often it has been noticed), some very perplexing questions would be presented as to the cause of the peculiarity. A rectangular figure, like that shown in fig. 82, would correspond to a cylindrical real figure; but it would also correspond to other figures of three dimensions. It is indeed possible that there may be no corona at all opposite the solar poles, the light we see there being merely a foreshortened view (ou this supposition) of the great extension over the spot belts. In this case the true figure of the corona would resemble that due to the rotation of two hyperbolas having the same axes, around one of these axes